<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #red{
            float:left;
            background-color:rgb(142, 31, 233);
            width:50px;
            height: 50px;
        }
        .green{
            background-color: blue;
            width:200px;
            height: 200px;
        }
        /* #f{
            border:solid;
            margin:10px;
            padding:10px;
        } */
        /* div{
             display:grid; 
        } */
    </style>
</head>
<body>
    <div  id="f">
        <div id ="red">浮动盒子</div>
        <div class="green"></div>
    </div>
</body>
</html>